<template>
	<div class="list">
		<div 
			class="item" 
			v-for="(item, key) of letters" 
			:key="item"
			:ref="item"
			@touchstart="handleTouchStart"
			@touchmove='handleTouchMove'
			@touchend='handleTouchEnd'
			@click="handleLetterClick"
		>
			{{item}}
		</div>
	</div>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
		letters () {
			const letters = []
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updated () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change', e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if (this.touchStatus) {
				if (this.timer) {
					clearTimeout(this.timer)
				}
					this.timer = setTimeout(() => {
						 const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
         	 }
					}, 16)
      }
		},
		handleTouchEnd () {
			this.touchStatus = false
		}
	}
}
</script>

<style lang='stylus' scoped>
	@import '~styles/varibles.styl'
	.list 
		display: flex
		flex-direction: column
		justify-content: center
		position: absolute
		top: 1.58rem
		right: 0
		bottom: 0
		width: .4rem
		.item
			text-align: center
			line-height: .4rem
			color: $bgColor
			
</style>